1. Field of the Invention
The present invention relates to a progressive safety gear for elevators consisting of a carrier, which is positioned in a transverse direction to the guide rail and which encompasses one guide rail for an elevator car, on which two brake shoes which are positioned one on each side of the guide rail are supported. One of the brake shoes functions as a passive brake shoe and the other as an active brake shoe. The active brake shoe is supported on an eccentric which is fastened to a cam in such a way that it rotates with it. The cam and the eccentric are able to rotate about a common center.
2. Discussion of the Prior Art
A progressive safety gear of the type mentioned above is already known from German reference DE 21 39 056. In this safety gear the blocked governor rope actuates a tripping lever on the safety gear which causes the tensioning eccentric fastened to the positioning eccentric to rotate. As a result, the tensioning eccentric comes into contact with the guide rail. As a result of this, and because the elevator car is still moving, the tensioning eccentric continues to rotate of its own accord due to the friction contact with the guide rail, and the active brake shoe is moved into the braking position via the positioning eccentric. In the braking position, the positioning eccentric has reached the end position before the greatest distance from the guide rail, because in this position the tensioning eccentric, due to the shape of its external contour, has reduced or lost its friction contact with the guide rail and is therefore no longer caused to rotate.
However, this progressive safety gear functions only in one direction, either up or down, and it is not possible in all necessary cases to release it by moving the car in the direction opposite to the direction in which it fell. This means that the safety gear cannot always be simply released after it has engaged.
A progressive safety gear which also works with an eccentric is the safety gear BFx3 of the East German elevator industry (Liftreport, Issue 5, 1991). When this progressive safety gear is tripped, two cams with rolling and sliding surfaces are rotated either counter-clockwise or clockwise depending on the direction of travel of the elevator, which causes in the downward travel direction a strong, and in the upward direction a weaker, braking deceleration of the elevator car. Tripping takes place by means of a governor rope passing over a separate pulley which, by transmitting its rotational movement, causes the eccentric to rotate in one direction or the other depending on the direction of travel. If braking takes place in the upward direction the angle of rolling and the radius to the sliding surface in the braking position is smaller than when braking takes place in the downward direction. This results in a different degree of compression of the braking springs and correspondingly the desired different braking forces for the two directions of travel.
A disadvantage of this device is that the controlling surfaces and the braking surface are on the same component, because of which the braking surface has a relatively small contact surface, which after several trippings as a result of wear can lead under certain circumstances to a reduced braking effect or even to faulty functioning. The complete eccentric must then be replaced. Furthermore, because of the additional rotational transmission device, an elaborate and relatively expensive triggering device is necessary.